THE  UNIVERSITY 
OF  ILLINOIS 


NON  CIRCULATING 

CHECK  FOF  :-JND 

CIRCUL, 


UNIVERSITY   OF   ILLINOIS, 

Agricultural  Experiment  Station 

CHAMPAIGN,  SEPTEMBER,  1893. 


BULLETIN  NO.  27. 

SOME    NEW  POINTS    IN   THE  MANIPULATION   OF  THE 
BABCOCK  MILK  TEST. 

Testing  milk  by  Dr.  Babcock's  method  has  generally  been  consid- 
ered a  very  simple  process.  The  details  of  the  method  were  so  elabo- 
rately and  carefully  worked  out  by  him,  before  publication,  that  no 
improvements  in  the  chemical  reactions  have  been  suggested  to  make 
the  process  any  more  useful  or  successful  than  when  first  described. 
Beginners  have  found,  however,  that  to  make  an  accurate  test  of  milk 
requires  somewhat  more  attention  "than  is  necessary  to  turn  the  crank  of 
a  churn.  Many  who  have  used  the  process  have  had  more  or  less 
trouble  from  foreign  substances,  either  black  or  white,  separating  with 
the  fat.  These  make  an  obscure  reading  of  the  per  cent  of  fat  because 
of  the  indistinct  separation  of  the  liquids.  The  common  remedy  sug- 
gested for  this  difficulty  has  been  a  change  of  acid.  If  there  is  "  black 
stuff  "  in  the  fat,  get  a  weaker  acid;  if  a  white  curd  separates  in  the  fat 
column,  change  to  a  stronger  acid.  That  a  too  strong  or  a  too  weak 
acid  may  cause  this  trouble  is  undoubtedly  correct  in  many  cases,  but  not 
always.  The  manipulation  of  the  test  may  also  cause  these  defects. 

It  was  found  by  the  writer  that  nearly  if  not  all  the  acid  sold  in 
Chicago  for  this  purpose  was  made  at  one  factory,  and  by  conversation 
with  the  manufacturer  it  was  learned  that  the  still  making  this  acid  was 
running  day  and  night,  turning  out  the  same  quality  of  acid  without 
change. 

It  has  generally  been  supposed  to  be  easier  to  test  a  mixture  of  the 
milk  of  several  cows  than  the  milk  of  one  cow,  and  that  possibly  there 
might  be  found  a  cow's  milk  which  could  not  be  successfully  tested. 
The  observations  given  in  this  article  are  the  results  of  a  great  many 
experiments  made  with  the  milk  of  each  of  the  seventy-five  cows  now 
in  the  dairy  test  at  the  World's  Columbian  Exposition. 

245 


246  BULLETIN   xo.   27.  [September, 

Since  May  ist  we  have  made  at  least  150  tests  of  milk  every  day. 
During  this  time  samples  of  a  great  variety  of  milks  have  been  tested. 
There  have  been  great  variations  in  the  composition  of  these  milks  and 
in  the  characteristics  and  health  of  the  cows.  We  have  been  able  to 
test  successfully  any  milk  yet  received,  and  by  proper  manipulation,  to 
get  a  very  clear  separation  of  the  fat. 

A  bad  separation  is  not  always  caused  by  the  strength  of  the  sul- 
phuric acid.  Our  work  has  demonstrated  that,  by  slight  changes  in  the 
manipulation,  at  least  three  kinds  of  tests  can  be  made  of  one  sample  of 
milk  with  the  same  acid. 

First,  a  test  giving  a  very  clear  separation  of  fat;  second,  a  separa- 
tion of  fat  which  contains  more  or  less  of  a  black,  flocculent  substance, 
especially  at  the  bottom  of  the  fat  column;  and,  third,  a  test  very  much 
like  the  second,  except  that  a  white,  instead  of  a  black,  substance  inter- 
feres with  a  clear  measurement  of  the  fat. 

The  black  substance  that  appears  is  probably  charred  fat  and  indi- 
cates too  strong  an  action  of  the  acid  on  the  milk.  The  white  adultera- 
tion of  the  fat  shows  either  too  weak  a  reaction  or  an  incomplete 
separation  by  the  centrifuge.  Each  of  these  defects  can,  of  course,  be 
produced  by  acid  either  very  much  too  strong  or  too  weak.  They  can 
also  be  brought  out,  by  different  manipulation,  when  acid  having  the 
correct  strength  is  used. 

If  the  acid  is  so  poured  into  the  milk  in  the  test  bottle  that  it  passes 
through  the  milk,  instead  of  following  down  the  inside  walls  of  the  test 
bottle,  a  portion  of  the  milk  is  thus  acted  on  by  the  strong  acid  before 
it  becomes  diluted  with  the  water  in  the  milk.  This  makes  a  more 
intense  action  of  the  acid  on  a  small  part  of  the  milk,  and  the  fat  it  con- 
tains is  somewhat  decomposed  and  blackened.  This  black  substance  is 
then  separated  with  the  fat  by  the  usual  method  of  finishing  the  test 
and  makes  the  measurement  of  the  fat  uncertain. 

Another  cause  of  the  "black  stuff"  in  the  fat  is  too  warm  milk. 
Sulphuric  acid,  sp.  gr.  1.82,  may  work  all  right  for  testing  milk  when 
both  "acid  and  milk  are  at  a  temperature  of  60°  F.;  but  if  the  weather 
changes,  or  the  testing  is  made  in  a  warm  room  where  the  temperature  is 
up  to  80°  or  90°  F.,  a  great  deal  of  black  stuff  may  be  found  in  the  fat. 

The  action  of  the  acid  on  the  milk  will  be  more  or  less  intense, 
according  to  the  temperature  of  the  liquids.  Persons  who  have  tested 
milk  throughout  the  year,  at  creameries  or  other  places,  may  have 
noticed  that  in  winter  the  fat  is  often  light  colored  or  whitish,  while  in 
summer  it  is  deeper  yellow.  This  variation  in  color  is  caused  by  the 
difference  in  the  temperature  of  the  milk  and  acid  as  well  as  the  strength  of 
the  acid.  Cooling  the  milk  in  the  test  bottles,  before  adding  acid,  will 
often  prevent  the  formation  of  the  black  substance  which  appears  in  the 
column  of  fat. 

The  white,  curdy  substance  that  sometimes  separates  with  the  fat 
can  be  destroyed  either  by  adding  the  hot  water  necessary  to  bring  the 


1893-]  MANIPULATION    OF    BABCOCK     MILK    TEST.  247 

fat  into  the  neck  of  the  test  bottle,  in  two  portions,  and  whirling  the 
test  bottle  in  the  centrifuge  after  each  addition  of  the  water,  or  by 
warming  the  milk  in  the  test.bottles,  so  that  it  will  be  about  80°  F.  when 
the  acid  is  added. 

It  is  my  opinion  that  returning  the  supply  of  acid  to  the  party  from 
whom  it  was  bought  is  often  unnecessary.  Any  person  who  has  trouble 
from  either  the  black  or  white  substance  separating  with  the  fat  can  prob- 
ably remedy  the  difficulty  by  some  changes  in  the  manipulation,  provided 
the  acid  is  anywhere  between  1.82  and  1.83  sp.  gr.  at  60°  F. 

No  exact  experiments  have  been  made  yet  to  determine  the  relation 
between  the  temperature  of  the  milk  and  acid,  and  the  sp.  gr.  of  the 
acid,  but  I  will  venture  to  guarantee  an  entirely  satisfactory  working  of 
the  Babcock  milk  test  if,  in  addition  to  the  elaborate  details  which  the 
originator  of  the  method  has  already  worked  out,  the  following  pre- 
cautions are  observed : 

First — An  acid  having  1.82  sp.  gr.  should  be  used  with  milk  at 
60°  to  70°  F.  If  the  acid  is  stronger,  cool  the  milk  to  a  lower  tempera- 
ture. Somewhat  weaker  acid  can  probably  be  made  to  work  all  right 
by  warming  the  milk. 

Second — When  measuring  the  acid  into  the  test  bottles,  hold  the 
bottle  at  an  angle  that  will  cause  the  acid  to  follow  the  inside  walls  to 
the  bottom  of  the  bottle  and  not  drop  through  the  milk  in  the  center  of 
the  bottle.  If  properly  poured  into  the  test  bottle  there  will  be  a  dis- 
tinct layer  of  milk  and  acid  with  little  or  no  black  color  between  them. 
Third — Thoroughly  mix  the  milk  and  acid  as  soon  as  measured 
into  the  test  bottle.  A  better  separation  of  fat  is  obtained  by  mixing  at 
once  than  by  allowing  the  two  liquids  to  stand  unmixed  in  the  bottle 
until  enough  tests  have  been  measured  out  to  fill  the  centrifuge. 

Fourth — After  five  minutes  whirling  of  the  test  bottles  in  the 
centrifuge,  add  hot  water  until  the  test  bottle  is  filled  up  to  the  neck 
only;  run  the  centrifuge  one  minute,  then  fill  the  neck  of  the  test  bottle 
with  hot  water  and  run  the  centrifuge  another  minute.  Adding  the 
necessary  hot  water  in  two  portions  is  often  a  great  help  in  getting  a 
clear  separation  of  fat.  When  the  test  bottles  are  taken  from  the  cen- 
trifuge they  are  put  into  water  at  140°  to  160°  F.,  and  the  per  cent  of 
fat  read  at  that  temperature. 

Fifth — Too  low  results  will  be  obtained  if  the  centrifuge  does  not 
have  sufficient  speed.  The  machines  have  to  be  watched,  as  constant 
use  wears  some  of  them  so  that  the  speed  designed  by  the  manufacturer 
is  not  obtained. 

Sixth — When  testing  skimmilks  or  buttermilks  which  have  a  very 
small  per  cent,  of  fat  (two-tenths  of  one  per  cent  or  less),  the 
reading  of  the  per  cent  of  fat  should  be  made  immediately  on  taking 
the  test  bottle  from  the  centrifuge.  If  this  is  not  done,  and  the  test 
bottle  cools  before  taking  the  reading,  the  contraction  of  the  liquid  in 
the  bottle  will  often  leave  the  fat  spread  over  the  inside  surface  of  the 


248  BULLETIN   NO.   27.  [ September,  1893. 

measuring  tube  so  that  it  is  not  seen  but  has  the  appearance  of  being 
only  a  dirty  tube.  If  read  when  taken  from  the  machine,  the  small 
globules  of  fat  can  be  seen  and  estimated. 

It  has  been  stated  by  foreign  critics  that  one  reason  why  they  did 
not  use  the  Babcock  milk  test  was  because  their  work  in  the  dairy  line 
had  been  done  for  years  by  the  old  methods  long  in  use,  and  in  order  to 
make  their  present  and  future  work  compare  with  the  past  they  must 
use  the  same  old  methods  of  their  fathers.  Our  work  for  the  past  two 
months  has  given  each  day  triplicate  proof  of  the  accuracy  of  the  Bab- 
cock  method  for  testing  milk.  The  milk  of  each  of  the  three  herds  of 
twenty-five  cows  is  creamed  and  churned  daily.  The  skimmilk  and 
buttermilk  are  tested,  and  the  butter  from  each  herd  analyzed  every  day. 
The  butter  fat,  found  by  testing  the  milk  of  each  of  the  twenty-five 
cows  in  each  herd,  is  nearly  all  accounted  for  by  the  analyses  of  the 
skimmilk,  buttermilk,  and  butter. 

The  records  show  that  from  June  ist  to  Aug.  3rd  there  has  been  an 
average  loss  in  fat  of  0.166,  o.  161,  and  0.153  per  cent  of  the  total  milk 
produced  by  the  three  herds.  This  small  loss  of  fat  by  the  manufacture 
of  milk  into  butter  demonstrates  that  if  this  method  is  correctly  used  in 
dairy  experiments,  and  the  results  of  such  investigations  are  not  com- 
parable with  those  of  the  past,  it  is  not  the  Babcock  milk  test  which  is 
wrong.  There  is  some  other  cause  for  the  discrepancy. 

E.  H.  FARRINGTON,  M.S., 

Chemist. 


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